noaccountdrifter

This truck will not start with ignition switch in start position but fires and runs great when started on compression. Ignition switch appears to be good. I suspect electronic control unit is not giving a go signal to the igniter. I am not familiar with troubleshooting this system and the Chilton and Haynes books do not provide specifics for this problem. I was not able to access a solution using the search on this site, so am asking for help, knowing that I may just not be proficient in using search and the answer is here, just can't find it as a Newbie.

Murcielago

A little more information would be helpful. Does the starter motor crank the engine over? Does it do so weakly? (If that's the case, your battery may not be strong enough to do that and power the fuel pump too.)

Could there be a switch on the clutch that disables the starter until the clutch is depressed? If there is such a switch, have you checked it?

How many miles on the car?

noaccountdrifter

Battery is charged, starter turns the engine fine. Could not find neutral safety switch or clutch operated switch, nor could I find such a switch in the Chilton/Haynes schematics. Fuel pump is add-on electric, as I suspect the cam lobe that drives the mechanical pump is worn. Truck has 224K miles. 22R engine. This problem started out intermittently and over a short period of time became constant. I have checked voltage on the circuit going to the ignition coil/igniter at the ignition switch and found 9 volts while engine is cranking. I have supplied external 12 volts to this circuit while cranking and still was not able to get the engine to fire. I do get voltage to the primary ignition circuit under all conditions, but no spark to the plugs except, as I mentioned, when I do not use starting circuit and start it on a hill on compression with the key turned to the on/run position.

Murcielago

This sounds like a tricky problem. But since your starter works, we can safely rule out clutch/ETC safety switches, since they disable the starter (so you don't run into something by trying to start in gear).

I just went out to look at my own truck, which is an 89, so likely similar to yours, but obviously not exactly the same. What I noticed is that the battery negative runs to the starter, and then a small ground wire runs from the battery to the body. What I'm thinking is that perhaps your engine or coil are weakly grounded. To test this thesis, if you have a jumper cable, connect the negative clip to some metal part of the engine, and connect the other side to the negative terminal on the battery. Try to start. If that doesn't work, try move the clip that's on the engine, and clip it to a body part near the coil. If that solves the problem, you have a weak ground. This isn't brilliant, but it's a quick and simple test.

You might think that this shouldn't happen, but when you're cranking your engine, you create a voltage drop due to the strain on the battery. And it's possible that with a weak ground, that voltage drop is enough to keep the negative side of the primary ignition circuit from getting sufficient juice.

If that doesn't help, I'm not sure what to suggest. Maybe this can become a "Car Talk" Puzzler.

Let us know what happens. Best of luck.

rokblok

iTrader: (1)

If it will "push start", the starter should start it. Either the battery is weak, starter is weak, or ignition switch is messed up in the "start" position.

noaccountdrifter

Thanks for all the good suggestions. I finally decided to follow the ignition troubleshooting instructions in the Chilton manual and found the ignition coil and igniter readings did not meet specs. I found a coil/igniter in my spare parts, replaced same and the truck is running fine.

wyoming9

iTrader: (1)

That makes no sense at all.

noaccountdrifter

It may not make sense unless we consider the possibility that the coil was weak/damaged and unable to generate a spark when the starter dropped the voltage. Starting on compression, there was no voltage drop and the coil was able to do its job.
Another possibility - if the internal circuitry of the igniter requires an input from the ecm when the starter is engaged perhaps that internal circuit was faulty, the replacement unit was not, and now the ignition is operating as designed.

The second guess is the one that I would go with, although I have no knowledge of just how the igniter works or of its internal components.